System of electric-motor control.



H. C. WALTER.

SYSTEM OF ELECTRIC MOTOR CONTROL.

APPLICATION FlLED MAY 27, 1912.

1,175,322. Patented Man-H, 1916.

34 x t g a b cde 3:? [2y 36 C INVENTOR and during HENRY C. "WALTER,

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ASSIGNOR T0 WESTINGHOUSE SYSTEM @F ELECTRIC-MOTORUQNTROL.

Specification of Letters Patent.

' Patented Mar. 314, 1916.

Application filed May 2?, 1912. Serial No. 700,034.

To all whom it may concern. v

Be it known that I, HENRY C. "WALTER, a citizen of the United States,and a resident of Pittsburgh, in the county of Allegheny and State ofPennsylvania, have inventeda new and useful Improvement in Systems ofElectrie-Motor-Control, of which the following is a specification.

My invention relates to methodsof and systems for controlling electricmotors and it has special reference to the control of local orregenerative braking circuits for direct current motors;

One object of my invention is to provide,

a controller of the class above indicated,

1n automatic means, depedent upon the speed of the motor, for regulatingthe flow of current in a regenerative braking circuit.

Another object of my invention is to provide a simple method forautomatically governing the braking of electric motors.

Controllers for electric motors have heretofore been arranged toestablish a local regenerative braking circuit in which the electricenergy generated in the motor armature during the braking period isconsumed.

The degree of braking secured in this manner has been directly dependentupon the speed of the motor armature and inversely dependent upon theresistance included in the braking circuit. \Vhen the motor operated athigh speeds, considerable resistance was therefore inserted in thebraking circuit and some means was provided for either manually orautomatically reducing the resistance as the speed of the motordecreased, in order to maintain a substantially constant braking force.

According to my present invention, I provide a braking circuit which isso connected to the motor armature as to receive alternating-currentenergy, and .I introduce such a reactance, or combination of reactanceand resistance, as to automatically effect the desired braking,irrespective of the motor speed when the braking circuit is completedthe entire braking period.

My invention relies upon the fact that the value and effectiveness ofreactance depends upon the frequency of the alternating current in thecircuit with which it is associated.

Figure l of the accompanying drawings is a diagrammatic View of a systemof control embodying and adapted for practicising my invention. Fig. 2is a simple diagram showing only the regenerative braking circultconnections. Fig. 3 is a view, corresponding to Fig. 2, of a modifiedarrangement which also embodies my invention.

Referring to Figs. 1 and 2 of the drawings, a direct current electricmotor having an armature 1, and field magnet windings 2 and 3 isgoverned by a plurality of independently operated switches 4 to 9,inclusive, which, in turn, are controlled by a master switchlO. Themaster switch is adapted to occupy a plurality of motor-operatingpositions a, Z), c, d and e, a single braking position x and an offposition 0. In addition to the usual commutator cylinder 11 and itsbrushes 12 and 13, the armature 1 is provided with a pair of collectorrings 14 and 15 which are connected to suitable points in the armaturewinding. When the switch 4 is closed, a circuit is completed from abrush 16, which engages the ring 14, through a conductor 17, the switch4, a conductor 18, an adjustable reactance member 19, and adjustableresistance member 20 and a conductor 21 to a brush 22 which engages thering 15. In starting the motor, resistor sections 23, 24, 25 and 26 areincluded in circuit with the motor armature in the usual manner, andthey are successively short circuited as the switches 6 to 9, inclusiveare closed.

The operation of the system is as follows: Assuming that the switchesoccupy the positions indicated in the drawing, if the master switch 10is moved into position a, a circuit is established from a line conductor27, through shunt field magnet winding 2 to an opposite line conductor28. An armature circuit is established from the conductor 27, throughthe commutator brush 13, the armature winding, the commutator brush 12,the conductor 29, the series field magnet winding 3, a conductor 30, thereslstor sect1ons26 to 23, inclusive, and the switch 5-which is closedin this position of the master switchto the line conductor a terminal 31of a 28. As the master switch successively occupies positions 6, 0, (Zand e, switches 6, 7, 8 and 9. are successively closed and the resistorsections 23, 24, 25 and 26 are successively short circuited, leaving themotor armature and the series field magnet winding connected across thecircuit. In order to stop the motor regardless of its speed ofoperation, it is only necessary to return the master controller to theoff position 0 and move it into the braking position as. In thisposition, a control circuit is established from storage batter 32, orfrom some other suitable source 0 energy, through a conductor 33, acontact finger 34, contact segments 35, a contact finger 36, a conductor37 a coil 38 of the switch 4 and a conductor 39 to an opposite terminal40 of the battery. When coil 38 is energized,

switch 4 is closed and the braking circuit is established, as aboveindicated. The intensity of the braking action will, of course, bedependent upon the current, which trav erses the braking circuit and thearmature winding, and is determined by the speed of the motor and theactive portions of the resistance member 20 and the reactance member 19.The value of the reactance will antomatically vary with the speed of themotor, since the reactance is always dependent upon the frequency of thealternating current which is supplied to the reactance member.

Any desired retardation of the motor may therefore be secured byproperly proportioning and adjusting the resistance member 20 and thereactance member 19. This is evident from a consideration of the factthat if the motor armature is rotating at relatively high speedswhen thebraking circuit is established, the value of the reactance will begreat, whereas its value will be relatively small if the armature speedis low. Consequently, during the braking period, the effect ofthereactance of the member 19 is to prevent an excessive currenttraversing the braking circuit when the motor is operating at highspeeds and its counter electromotive force is high and, at thesame'time, to permit a sufficient braking current to secure the desiredbraking action when the speed and counter-.electromotive force of themotor have been materially reduced.

Referring to Fig. 3 of the drawings, according to the arrangement hereshown three collector rings 41, 42 and 43 are substituted for the rings14 and 15 and a starconnected three-phase braking circuit is substitutedfor the single phase braking circuit of Fig. 1. With the three-phasearrangement, three reactance members 44, 45

and 46 and three resistance members 47, 48 and 49 are utilized, onereactance member and one resistance member being located in each branchof the three-phase circuit. I believe the braking efl'ect will besomewhat enhanced by utilizing the three-phase arrangement, but thesingle-phase arrangement is, of course, simpler and is almost equallyeffective.

That portion of the controller which has to do with the acceleration ofthe motor forms no part of my present invention and may be replaced byany suitable manually operated or automatic controller. It is alsoevident that the circuit connections of the system may be modifiedwithin the spirit and scope of my invention.

My invention is not restricted to a compound wound motor, but isapplicable to various types of dynamo electric machines.

I I claim as my invention:

1. The method of braking a direct-current motor which consists inestablishing a local alternating-current circuit comprising the motorarmature and opposing the flow of current in said circuit by an externalreactive impedance.

2. The method of braking a direct-current electric motor which consistsin establishing a local alternating-current circuit including the motorarmature and opposing the flow of current in said circuit by apredetermined combination of resistance and reactance.

3. The method of braking a direct-current electric motor which consistsin establishing a local alternating-current circuit comprising the motorarmature and opposing the new of current in said circuit in accordancewith the speed of said motor.

4. A braking system comprising a directcurrent electric motor havin anarmature windin an external reactive impedance and means tor completingan alternating-current local circuit including the armature winding andthe impedance.

5. A braking system comprising an electric motor having an armatureWinding, collector rings connected to suitable points therein, brushesengaging the rings, an external reactive impedance, and means forconnecting the impedance across the collector rings during the brakingperiod.

6. A braking system comprising adirect current electric motor having anarmature winding and a commutator cylinder, means.

' for including resistance in the armature cir current electric motorhaving an armature subscribed my name this 24th day of May Winding, ofmeans for establishing a local 1912. alternating-current circuitincluding said Winding and means for opposing the flow of HENRY WALTER 5current in said circuit in accordance With- Witnesses:

the speed of said motor. F. A. Rnw,

In testimony whereof, I have hereunto B. B. Hume.

